Next thing we hear is Meredith arguing with him that this is actually a big deal and she worries that he's putting too much pressure on himself. Derek assures her he'll be done by the mysterious 5:00 appointment; when she asks if he really needs today to be his first day back he tells her that he especially needs it to be today. They smooch, so we know they are doing okay.
Callie is sitting next to someone's hospital bed, telling them about how Derek is now ready. But when the camera pulls back, what we see is pretty much completely horrible -- she's talking to Mark, who is unconscious and on a ventilator. Callie seems a little bit unsure about Derek's decision but she shuts up when he enters the room and changes the subject, telling him she keeps hoping that if she says something big enough, Mark will open his eyes. She's hoping against hope because it turns out that Mark had a very clear directive that if he was out for 30 days with no signs of recovery, he wanted to be let go. Five o'clock that evening will be 30 days, and they have to honor his wish and turn off the machines. Callie knows this intellectually, but it's understandable that she still hopes he'll come back to them. She leans in and breathily starts to talk about how hot it is, so she has to take off her shirt and doesn't it feel better now with her boobs out? It's kind of hilariously bittersweet since it's what Mark would have loved to hear, but he's gone. Derek notes that if that won't wake him, he doesn't know what will. Once Callie leaves, Derek looks at his friend's form and sadly chides him for always having to be first.
Onscreen, a card rewinds from 2012 to 1994, and we see what appears to be a home video taken of the guys while they get ready for Derek's wedding. Derek jokes that Mark is a terrible best man. Dude, just wait until he sleeps with your wife in a few years. Mark keeps teasing Derek that guys that look like them were meant to be with tons of women, not just one for the rest of time. They seem not to know this video is being taken, which gives it a creepy whiff of Eau de Voyeur. After Mark comments that Derek will never find a friend as good as him, he notices whoever it is filming, and the camera drops as Mark goes after him. This year, the title card and "created by" card are, like AC/DC, back in black. Even though I always hated the white, the black feels very somber right now.
The next thing we see is a home video from 2007, with Callie waiting in bed while Mark fiddles with the camera. She's very against the idea of filming whatever magic is about to take place, no matter how much Mark sexily protests that she'll want to relive it. They start to kiss and then she pauses just a moment so that she can throw a pillow at the camera and knock the power off.